Dan Coby wrote:
J. Clarke wrote:
Lew Hodgett wrote:
"J. Clarke" wrote:

If he's using 130v bulbs on 120v then he's using about 15% less KWH
than he
would be using 120v of the same nominal wattage.
-------------------------------------
NOT!

100 watts is 100 watts regardless the voltage rating of the lamp.

The current flowing thru the lamp is reduced which reduces lumen
output when the voltage rating of the lamp is increased.

(E = I*R for a resistance load.)

If you have visions of becoming an electrical engineer, don't quit
your day job.

For a resistive load P=E^2/R. If the lamp is rated for 100 watts at
130 volts then it will dissipate (120^2/130^2)*100 watts at 120v or
about 85 watts if its resistance remains constant.

The assumption that the resistance will remain constant is a bad one.
As has already been pointed out elsewhere in this thread, the
resistance of a light bulb varies with the temperature of the
filament. A colder filament will have a lower resistance. A lower
resistance will result in a higher current and
a higher power. The actual power at 120 volts will be somewhere
between the 85 watts that you calculated and the 100 watts that it
would dissipate at 130 volts.

The standard number given is V^1.6. But the point is that a 100 watt bulb
only draws 100 watts at the design voltage, it's not 100 watts at all
voltages as Brainiac claims.